The purpose of the proposed work is to determine the contribution of genetic factors to the variation in the isoantibodies and the immunoglobulins (G, M, A, E) and to identify other causes of variation affecting the levels of these proteins in a natural population. The degrees of interrelations among the levels of the different classes of immunoglobulins and the isoantibodies will also be established. In addition to the study of variation in a natural population, families with allergic children will be selected and studied in order to evaluate variation in the immunoglobulins as a possible factor in the predisposition to childhood allergies. BIBLIOGRAPHIC REFERENCE: Grundbacher, F.J. Causes of Variation in serum IgE levels in normal populations. J. Allergy Clin. Immunol. 56:104-111, 1975.